Because optical materials formed from synthetic resin are light compared to inorganic materials such as glasses, excellent in molding processability and the like, and easy to handle, such optical materials have been widely used in various applications in recent years. Polystyrene resin, polymethylmethacrylate resin, polycarbonate resin, diethylene glycol diallyl carbonate resin, and the like have been heretofore used as such resin for organic optical materials.
However, previous resins for organic optical materials are not always satisfactory because these resins have drawbacks such as a low refractive index, a high birefringence, a high dispersibility, and the like; and are also poor in heat resistance and shock resistance. In particular, diethylene glycol diallyl carbonate resin (CR-39) and the like used as lens materials have a low refractive index (1.50). Therefore, when these resins are used as lenses, the edge thickness and the central thickness become thick, causing drawbacks such as degradation in the appearance of the lenses and an increase in the weight.
Consequently, attempts have been made to improve the refractive index of resin for organic optical materials. For example, as a monomer for producing resin having a high refractive index and excellent transparency, Patent Literature 1 and Patent Literature 2 listed below disclose a diaryl sulfide compound represented by the following chemical formula (a):
wherein R1 and R2 are hydrogen or methyl.
Likewise, as a monomer for producing resin having a high refractive index and excellent transparency, Patent Literature 3 listed below also discloses a diaryl sulfide compound represented by the following chemical formula (b):

While these diaryl sulfide compounds are described as monomers for producing resin having a high refractive index and excellent transparency, the production of these compounds requires a 4,4′-dimercaptodiaryl sulfide compound, which is an expensive compound represented by the following chemical formula:

Accordingly, the diaryl sulfide compounds of the above chemical formulae (a) and (b) obtained using the above-mentioned compound as a starting material are costly, and the economic efficiency thereof is low. Therefore, there is a demand for a less-expensive material as a monomer that can be used for producing resin having a high refractive index and excellent transparency.